The present invention relates to portable power planers and in particular to an improved depth of cut adjustment mechanism for a power planer. In general, portable power planers comprise a motor driven rotary cutter head having one or more cutting blade assemblies disposed thereon for performing a planing operation on the surface of a workpiece as the cutter head rotates. The bottom surface of the tool consists of a fixed shoe located rearwardly of the cutter head and an adjustable shoe disposed forwardly of the cutter head. As the front shoe is adjusted upwardly or downwardly the cutting depth of the cutting blade of the planar is adjusted accordingly.
The adjustable front shoe of a portable power planer typically includes an integral stem or sleeve that is threaded either directly to an adjustment cap disposed atop the front end of the housing or to a threaded shaft or bolt that is in turn fastened at its other end to the adjustment cap for rotation therewith. In either arrangement, however, a powerful compression spring is interposed about the sleeve between the shoe and the housing to maintain the elevation of the adjustable shoe in the position set by the operator. The compression spring is held in compression between the adjustable shoe and the housing and must be of sufficient strength to resist the natural tendency of the operator to bear down upon the planer when performing a planing operation, and yet be sufficiently compressible to permit convenient upward adjustment of the adjustable front shoe. As a consequence, in some planers having conventional depth of cut adjustment mechanisms, the operator can overcome the thrust force of the compression spring and dislodge the adjustable shoe from its preset position, thereby causing an undesired variation in the depth of cut.
Accordingly, it is the primary object of the present invention to provide an improved depth of cut adjustment mechanism for a portable power planer which accurately maintains the preset position of the adjustable shoe when the operator bears down upon the tool.
Additionally, it is an object of the present invention to provide such a depth of cut adjustment mechanism for a power planer which utilizes a tension spring which works with the operator to take up the tolerance play at the interface between the adjustable shoe and the tool housing.
Furthermore, it is an object of the present invention to provide such a depth of cut adjustment mechanism for a power planer that substantially reduces the space required within the tool housing, as well as the manufacturing cost of the tool, as compared to conventional prior art constructions.
In general, the elevation adjustment arrangement according to the present invention includes an adjustable shoe having fixedly attached thereto a rod extending upwardly therefrom which is threadedly engaged at its upper end to an elevation positioning nut rotatably mounted in the housing and fixed against elevational movement relative thereto. An adjustment cap disposed atop the housing is affixed to the positioning nut so that rotation of the adjustment cap results in elevational movement of the adjustable front shoe. A tension spring is connected between the front end of the adjustable shoe and the housing to cancel out tolerance play between the adjustable shoe and the housing. Because the tension spring works with the operator as he bears down upon the tool, no unwanted movement or wobble of the adjustable front shoe results.
In addition, the preferred embodiment of the present invention includes means for calibrating the elevation adjustment mechanism so that when the scale provided on the adjustment cap reads zero, the adjustable shoe is set for zero cutting depth. A positive park position is also provided which when engaged sets the adjustable shoe below zero elevation so that the cutting blades will not mar the surface upon which the tool is placed.
Additional objects and advantages of the present invention will become apparent from a reading of the detailed description of the preferred embodiment which makes reference to the following set of drawings in which :